Brain Teaser Challenge Solution - June 2008 Butch Shadwell
Last month I discussed the high cost of gasoline and the impact on holiday travel. I decided it would be useful to talk about ways to get a better value for your gasoline dollar. So I asked this question. “Most cars have two or three pedals on the floor. This month I am asking you to tell me which one is the cause of the most loss of fuel economy.”
First we must accept the constraints that the vehicle will be operated safely and within the requirements of traffic laws. No energy saving strategy may violate this axiom.
So, an automobile is a machine designed to convert chemical potential energy into kinetic energy. As you depress the gas pedal, the machine proceeds to do this function at various rates (different rates of acceleration, or overcoming friction and air resistance) and with varying efficiency. In general as you do this, the efficiency of energy conversion into useful momentum is always significantly higher than zero, even if you accelerate too quickly, which is wasteful. You continually get movement of the car down the road in exchange for your fuel dollar.
As you press the brake pedal, the braking system converts the vehicles valuable kinetic energy (momentum) into waste heat, which is dissipated into the atmosphere and the road. These petro-dollars are actually burned as 100% heat pollution. It is not an exaggeration to imagine your fuel dollars being burned by your brake pedal. No value for these dollars.
So it is clear that the thrifty driver will drive in a fashion that uses the gas pedal judiciously (don’t push it down too far), but the main one to avoid is the brake pedal (except when you are stopped). Don’t follow so closely to the car in front of you, so that you can avoid having to apply the brake as their speed varies. As soon as the traffic light turns yellow, take your foot off of the gas pedal. There is no reason to keep pumping dollars into the cars momentum when it will all be wasted by the brake pedal as you stop for the red light.
I would really enjoy discussing the effects on fuel economy of using the clutch pedal, but this column is getting too long. Maybe next time.
Brain Teaser Challenge – July 2008 Butch Shadwell
We bought a new 61” HDTV last Christmas. It is the DLP type, though it has some interesting innovations. Instead of the usual projector lamp and color wheel for the light source, this set uses three high output LEDs (red, green, and blue). No color wheel and motor and no projector lamp to replace. Incase you are not familiar with DLP TVs, DLP stands for digital light processing. It is based on the use of a MEMS (micro electro mechanical system) device with 2,073,600 tiny mirrors that can be electro-statically moved. The mirrors are adjusted 360 times per second successively displaying the red, green, or blue components of the image, so that we get up to 120 complete display frames per second. The amount of red, green or blue light that is added to an individual pixel (picture element) by its respective mirror, is controlled by how long the mirror allows that color light to project to the screen. Each mirror pulse width modulates the light to control how much red is blended with how much green and blue. Your eye integrates these pulsing light sources into 10,000 levels of brightness for each of the three color components.
Let’s say that my high output LEDs have a forward voltage drop of 4 volts at 25 degrees C at the junction and the forward voltage drops 3mV per degree C. Then I supply forward current to one of these LEDS through a 100 ohm resistor and a 10VDC source. So tell me the current through the LED when the junction gets up to 100 degrees C? I know this is a simple one, but I have been struggling with writers block. Good luck.
Reply to Butch Shadwell at b.shadwell@ieee.org (email), 904-223-4510 (fax), 904-223-4465 (v), 3308 Queen Palm Dr., Jacksonville, FL 32250-2328. (http://www.shadtechserv.com) The names of correct respondents may be mentioned in the solution column.
Brain
Teaser Challenge by Butch Shadwell
